High-frequency signal transmission line and electronic apparatus

ABSTRACT

An easily bendable high-frequency signal transmission line includes a dielectric body including a protection layer and dielectric sheets laminated on each other, a surface and an undersurface. A signal line is a linear conductor disposed in the dielectric body. A ground conductor is disposed in the dielectric body, faces the signal line via the dielectric sheet, and continuously extends along the signal line. A ground conductor is disposed in the dielectric body, faces the ground conductor via the signal line sandwiched therebetween, and includes a plurality of openings arranged along the signal line. The surface of the dielectric body on the side of the ground conductor with respect to the signal line is in contact with a battery pack.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to high-frequency signal transmissionlines and electronic apparatuses, and, more particularly, to ahigh-frequency signal transmission line including a signal line andground conductors facing the signal line and an electronic apparatus.

2. Description of the Related Art

As a high-frequency transmission line for connecting high-frequencycircuits, a coaxial cable is generally used. Since coaxial cables areeasily deformed (bent) and are inexpensive, they are widely used.

In recent years, high-frequency apparatuses such as mobile communicationterminals have been miniaturized. Accordingly, in such a high-frequencyapparatus, it is difficult to obtain the space required for a coaxialcable having a circular cross section. A high-frequency signaltransmission line obtained by forming a strip line in a flexiblelaminate is therefore sometimes used.

Triplate strip lines have a structure in which a signal line issandwiched between ground conductors. Since the thickness of such ahigh-frequency signal transmission line in a lamination direction issmaller than the diameters of coaxial cables, the high-frequency signaltransmission line can fit into a small space into which the coaxialcables cannot fit.

As an invention related to the high-frequency signal transmission line,a flexible substrate disclosed in Japanese Unexamined Patent ApplicationPublication No. 2007-123740 is known. In the flexible substratedisclosed in Japanese Unexamined Patent Application Publication No.2007-123740, since a ground conductor has an opening portion, a stripline can be more easily bent as compared with a strip line sandwichedbetween ground conductors formed on the entire surfaces.

However, in the flexible substrate disclosed in Japanese UnexaminedPatent Application Publication No. 2007-123740, an electromagnetic fieldmay exit from the opening portion to the outside of the flexiblesubstrate. In a case where an article, such as a dielectric or a metalbody, is disposed around the flexible substrate, electromagnetic fieldcoupling occurs between the signal line in the flexible substrate andthe article. As a result, the characteristic impedance of the signalline in the flexible substrate may deviate from a predeterminedcharacteristic impedance.

SUMMARY OF THE INVENTION

Preferred embodiments of the present invention provide a high-frequencysignal transmission line that can be easily bent and can significantlyreduce and prevent deviation of a characteristic impedance of a signalline included therein from a predetermined characteristic impedance, andalso provide an electronic apparatus.

A high-frequency signal transmission line according to a preferredembodiment of the present invention includes a laminate includinglaminated insulating layers, a first main surface and a second mainsurface, a linear signal line that is disposed in the laminate, a firstground conductor that is disposed in the laminate, faces the signal linevia one of the insulating layers, and continuously extends along thesignal line, and a second ground conductor that is disposed in thelaminate, faces the first ground conductor via the signal linesandwiched therebetween, and includes a plurality of openings arrangedalong the signal line. The first main surface located on a side of thefirst ground conductor with respect to the signal line is a surface tobe in contact with an article.

A high-frequency signal transmission line according to another preferredembodiment of the present invention includes an element assemblyincluding a first main surface and a second main surface, a linearsignal line disposed in the element assembly, a first ground conductorthat is disposed on a side of the first main surface with respect to thesignal line in the element assembly and faces the signal line, and asecond ground conductor that faces the first ground conductor via thesignal line sandwiched therebetween in the element assembly, andincludes an opening arranged along the signal line, an adhesive layerlocated on the first main surface, and a cover layer releasably attachedto the adhesive layer.

An electronic apparatus according to a preferred embodiment of thepresent invention includes the high-frequency signal transmission lineand an article. The high-frequency signal transmission line is fixed tothe article via the adhesive layer from which the cover layer has beendetached.

According to various preferred embodiments of the present invention, asignal line can be easily bent, and the deviation of the characteristicimpedance of the signal line from a predetermined characteristicimpedance can be significantly reduced and prevented.

The above and other elements, features, steps, characteristics andadvantages of the present invention will become more apparent from thefollowing detailed description of the preferred embodiments withreference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an external perspective view of a high-frequency signaltransmission line according to a first preferred embodiment of thepresent invention.

FIG. 2 is an exploded view of a dielectric body in the high-frequencysignal transmission line illustrated in FIG. 1.

FIG. 3 is a cross-sectional view of the high-frequency signaltransmission line illustrated in FIG. 1.

FIG. 4 is a cross-sectional view of a high-frequency signal transmissionline.

FIGS. 5A and 5B are an external perspective view and a cross-sectionalview of a connector in a high-frequency signal transmission line.

FIGS. 6A and 6B are plan views of an electronic apparatus including ahigh-frequency signal transmission line from a y-axis direction and az-axis direction.

FIG. 7 is a cross-sectional view of a portion C illustrated in FIG. 6A.

FIG. 8 is a cross-sectional view of a high-frequency signal transmissionline and a battery pack to which the high-frequency signal transmissionline is fixed with an installation method according to a firstmodification of the first preferred embodiment of the present invention.

FIG. 9 is a cross-sectional view of a high-frequency signal transmissionline and a battery pack to which the high-frequency signal transmissionline is fixed with an installation method according to a secondmodification of the first preferred embodiment of the present invention.

FIG. 10 is an external perspective view of the inside of an electronicapparatus in a case where an installation method according to a thirdmodification of the first preferred embodiment of the present inventionis used.

FIG. 11 is an exploded view of a laminate in a high-frequency signaltransmission line according to the first modification of the firstpreferred embodiment of the present invention.

FIG. 12 is a perspective view of the high-frequency signal transmissionline illustrated in FIG. 11 from the z-axis direction.

FIG. 13 is an equivalent circuit diagram of a portion of ahigh-frequency signal transmission line according to the firstmodification of the first preferred embodiment of the present invention.

FIG. 14 is an exploded view of a laminate in a high-frequency signaltransmission line according to the second modification of the firstpreferred embodiment of the present invention.

FIG. 15 is an exploded view of a laminate in a high-frequency signaltransmission line according to the third modification of the firstpreferred embodiment of the present invention.

FIG. 16 is an exploded view of a laminate in a high-frequency signaltransmission line according to a fourth modification of the firstpreferred embodiment of the present invention.

FIG. 17 is an exploded view of a laminate in a high-frequency signaltransmission line according to a fifth modification of the firstpreferred embodiment of the present invention.

FIG. 18 is a perspective view of the high-frequency signal transmissionline illustrated in FIG. 17 from the z-axis direction.

FIG. 19 is an exploded view of a laminate in a high-frequency signaltransmission line according to a sixth modification of the firstpreferred embodiment of the present invention.

FIG. 20 is a perspective view of the high-frequency signal transmissionline illustrated in FIG. 19 from the z-axis direction.

FIG. 21 is an external perspective view of a high-frequency signaltransmission line according to a second preferred embodiment of thepresent invention of the present invention.

FIG. 22 is an exploded view of a dielectric body in the high-frequencysignal transmission line illustrated in FIG. 21.

FIG. 23 is a cross-sectional view of the high-frequency signaltransmission line illustrated in FIG. 21.

FIG. 24 is a cross-sectional view of a high-frequency signaltransmission line.

FIG. 25 is a cross-sectional view of an electronic apparatus 200.

FIG. 26 is a cross-sectional view of a high-frequency signaltransmission line and a battery pack to which the high-frequency signaltransmission line is bonded.

FIG. 27 is an exploded view of a laminate in a high-frequency signaltransmission line according to a first modification of the secondpreferred embodiment of the present invention.

FIG. 28 is an exploded view of a laminate in a high-frequency signaltransmission line according to a second modification of the secondpreferred embodiment of the present invention.

FIG. 29 is an exploded view of a laminate in a high-frequency signaltransmission line according to a third modification of the secondpreferred embodiment of the present invention.

FIG. 30 is an exploded view of a laminate in a high-frequency signaltransmission line according to a fourth modification of the secondpreferred embodiment of the present invention.

FIG. 31 is an exploded view of a laminate in a high-frequency signaltransmission line according to a fifth modification of the secondpreferred embodiment of the present invention.

FIG. 32 is an exploded view of a laminate in a high-frequency signaltransmission line according to a sixth modification of the secondpreferred embodiment of the present invention.

FIG. 33 is an external perspective view of a high-frequency signaltransmission line according to a seventh modification of the secondpreferred embodiment of the present invention.

FIG. 34 is an exploded view of a dielectric body in the high-frequencysignal transmission line illustrated in FIG. 33.

FIG. 35 is a cross-sectional view of the high-frequency signaltransmission line illustrated in FIG. 33.

FIG. 36 is an external perspective view of a high-frequency signaltransmission line according to an eighth modification of the secondpreferred embodiment of the present invention.

FIG. 37 is an exploded view of a dielectric body in the high-frequencysignal transmission line illustrated in FIG. 36.

FIG. 38 is a cross-sectional view of the high-frequency signaltransmission line illustrated in FIG. 36.

FIG. 39 is an external perspective view of a high-frequency signaltransmission line according to a ninth modification of the secondpreferred embodiment of the present invention.

FIG. 40 is an exploded view of a dielectric body in the high-frequencysignal transmission line illustrated in FIG. 39.

FIG. 41 is a cross-sectional view of the high-frequency signaltransmission line illustrated in FIG. 39.

FIG. 42 is an exploded view of a dielectric body in a high-frequencysignal transmission line according to a tenth modification of the secondpreferred embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First PreferredEmbodiment

A high-frequency signal transmission line and an electronic apparatusaccording to the first preferred embodiment of the present inventionwill be described below with reference to the accompanying drawings.

The structure of a high-frequency signal transmission line according tothe first preferred embodiment of the present invention will bedescribed below with reference to the accompanying drawings. FIG. 1 isan external perspective view of a high-frequency signal transmissionline 10 according to the first preferred embodiment of the presentinvention. FIG. 2 is an exploded view of a dielectric body 12 in thehigh-frequency signal transmission line 10 illustrated in FIG. 1. FIG. 3is a cross-sectional view of the high-frequency signal transmission line10 illustrated in FIG. 1. FIG. 4 is a cross-sectional view of thehigh-frequency signal transmission line 10. FIGS. 5A and 5B are anexternal perspective view and a cross-sectional view of a connector 100b in the high-frequency signal transmission line 10. Referring to FIGS.1 to 5B, a lamination direction in the high-frequency signaltransmission line 10 is defined as a z-axis direction, a longitudinaldirection in the high-frequency signal transmission line 10 is definedas an x-axis direction, and a direction orthogonal to the x-axisdirection and the z-axis direction is defined as a y-axis direction.

For example, the high-frequency signal transmission line 10 preferablyis used to connect two high-frequency circuits in an electronicapparatus such as a mobile telephone. As illustrated in FIGS. 1 to 3,the high-frequency signal transmission line 10 includes the dielectricbody 12, an external terminal 16 (16 a and 16 b), a signal line 20,ground conductors 22 and 24, via-hole conductors b1, b2, B1, and B2, andconnectors 100 a and 100 b.

The dielectric body 12 extends in the x-axis direction in plan view fromthe z-axis direction, and includes a line portion 12 a and connectionportions 12 b and 12 c. The dielectric body 12 is a laminate obtained bylaminating a protection layer and dielectric sheets (insulating layers)18 (18 a to 18 c), which are illustrated in FIG. 2, in this order from apositive z-axis direction to a negative z-axis direction. In thefollowing description, the main surface of the dielectric body 12 in thepositive z-axis direction is referred to as a surface (first mainsurface) and the main surface of the dielectric body 12 in the negativez-axis direction is referred to as an undersurface (second mainsurface).

The line portion 12 a extends in the x-axis direction. The connectionportion 12 b is connected to the end of the line portion 12 a in anegative x-axis direction, and the connection portion 12 c is connectedto the end of the line portion 12 a in a positive x-axis direction. Theconnection portions 12 b and 12 c preferably are rectangular orsubstantially rectangular in shape, for example. The width of theconnection portions 12 b and 12 c in the y-axis direction is larger thanthat of the line portion 12 a in the y-axis direction.

The dielectric sheet 18 extends in the x-axis direction in plan viewfrom the z-axis direction, and preferably has the same or substantiallythe same shape as the dielectric body 12. The dielectric sheet 18 ismade of a thermoplastic resin such as polyimide or liquid crystalpolymer having flexibility. As illustrated in FIG. 4, a thickness T1 ofthe dielectric sheet 18 a is larger than a thickness T2 of thedielectric sheet 18 b. For example, after the dielectric sheets 18 a to18 c have been laminated, the thickness T1 is preferably in the range ofabout 50 μm to about 300 μm, for example. In this preferred embodiment,the thickness T1 preferably is about 150 μm, for example. The thicknessT2 preferably is in the range of about 10 μm to about 100 μm, forexample. In this preferred embodiment, the thickness T2 preferably isabout 50 μm, for example. In the following description, the main surfaceof the dielectric sheet 18 in the positive z-axis direction is referredto as a surface, and the main surface of the dielectric sheet 18 in thenegative z-axis direction is referred to as an undersurface.

The dielectric sheet 18 a includes a line portion 18 a-a and connectionportions 18 a-b and 18 a-c. The dielectric sheet 18 b includes a lineportion 18 b-a and connection portions 18 b-b and 18 b-c. The dielectricsheet 18 c includes a line portion 18 c-a and connection portions 18 c-band 18 c-c. The line portions 18 a-a, 18 b-a, and 18 c-a define the lineportion 12 a. The connection portions 18 a-b, 18 b-b, and 18 c-b definethe connection portion 12 b. The connection portions 18 a-c, 18 b-c, and18 c-c define the connection portion 12 c.

As illustrated in FIGS. 1 and 2, an external terminal 16 a preferably isa rectangular or substantially rectangular conductor disposed near thecenter of the surface of the connection portion 18 a-b. As illustratedin FIGS. 1 and 2, an external terminal 16 b preferably is a rectangularor substantially rectangular conductor disposed near the center of thesurface of the connection portion 18 a-c. The external terminals 16 aand 16 b are made of a metal material such as silver or copper havinglow resistivity, for example. The surfaces of the external terminals 16a and 16 b preferably are gold-plated.

As illustrated in FIG. 2, the signal line 20 is a linear conductordisposed in the dielectric body 12, and extends in the x-axis directionon the surface of the dielectric sheet 18 b. Both ends of the signalline 20 individually overlap the external terminals 16 a and 16 b inplan view from the z-axis direction. For example, the line width of thesignal line 20 preferably is in the range of about 100 μm to about 500μm, for example. In this preferred embodiment, the line width of thesignal line 20 preferably is about 240 μm, for example. The signal line20 is made of a metal material such as silver or copper having lowresistivity.

As illustrated in FIG. 2, in the dielectric body 12, the groundconductor 22 (first ground conductor) is disposed in the positive z-axisdirection with respect to the signal line 20, and, more specifically, isdisposed on the surface of the dielectric sheet 18 a nearest to thesurface of the dielectric body 12. The ground conductor 22 extends inthe x-axis direction on the surface of the dielectric sheet 18 a, andfaces the signal line 20 via the dielectric sheet 18 a. Substantially noopening is disposed at the ground conductor 22. That is, the groundconductor 22 is a solid electrode that continuously extends in thex-axis direction along the signal line 20 in the line portion 12 a. Theground conductor 22 does not necessarily have to completely cover theline portion 12 a. For example, in order to let gas generated by heatbonding of the dielectric sheet 18 made of a thermoplastic resin escape,a small hole may be provided at a predetermined position on the groundconductor 22. The ground conductor 22 preferably is made of a metalmaterial such as silver or copper having low resistivity, for example.

The ground conductor 22 includes a line portion 22 a and terminalportions 22 b and 22 c. The line portion 22 a is disposed on the surfaceof the line portion 18 a-a, and extends in the x-axis direction. Theterminal portion 22 b is disposed on the surface of the line portion 18a-b, and preferably is a rectangular or substantially rectangular ringsurrounding the external terminal 16 a. The terminal portion 22 b isconnected to the end of the line portion 22 a in the negative x-axisdirection. The terminal portion 22 c is disposed on the surface of theline portion 18 a-c, and preferably is a rectangular or substantiallyrectangular ring surrounding the external terminal 16 b. The terminalportion 22 c is connected to the end of the line portion 22 a in thepositive x-axis direction.

As illustrated in FIG. 2, in the dielectric body 12, the groundconductor 24 (second ground conductor) is disposed in the negativez-axis direction with respect to the signal line 20, and, morespecifically, is disposed on the surface of the dielectric sheet 18 c.The ground conductor 24 is therefore disposed between the dielectricsheets 18 b and 18 c. The ground conductor 24 extends in the x-axisdirection on the surface of the dielectric sheet 18 c, and faces thesignal line 20 via the dielectric sheet 18 b. That is, the groundconductor 24 faces the ground conductor 22 via the signal line 20sandwiched therebetween. The ground conductor 24 preferably is made of ametal material such as silver or copper having low resistivity, forexample.

The ground conductor 24 includes a line portion 24 a and terminalportions 24 b and 24 c. The line portion 24 a is disposed on the surfaceof the line portion 18 c-a, and extends in the x-axis direction. Theline portion 24 a has a ladder shape obtained by alternately disposing aplurality of openings 30 at which no conductive layer is provided and aplurality of bridge portions 60 at which a conductive layer is arrangedalong the signal line 20. As illustrated in FIGS. 2 and 4, the openings30 preferably are rectangular or substantially rectangular in shape andoverlap the signal line 20 in plan view from the z-axis direction.Accordingly, the signal line 20 alternately overlaps the openings andthe bridge portions 60 in plan view from the z-axis direction. Theopenings 30 are arranged at regular intervals.

The terminal portion 24 b is disposed on the surface of the line portion18 c-b, and preferably is a rectangular or substantially rectangularring. The terminal portion 24 b is connected to the end of the lineportion 24 a in the negative x-axis direction. The terminal portion 24 cis disposed on the surface of the line portion 18 c-c, and preferably isa rectangular or substantially rectangular ring. The terminal portion 24c is connected to the end of the line portion 24 a in the positivex-axis direction.

As described previously, the signal line 20 is sandwiched between theground conductors 22 and 24 via the dielectric layers 18 a and 18 b.That is, the signal line 20 and the ground conductors 22 and 24 define atriplate strip line structure. As illustrated in FIG. 4, the distancebetween the signal line 20 and the ground conductor 22 is substantiallyequal to the thickness T1 of the dielectric sheet 18 a, and, forexample, is preferably in the range of about 50 μm to about 300 μm, forexample. In this preferred embodiment, the distance between the signalline 20 and the ground conductor 22 preferably is about 150 μm, forexample. On the other hand, as illustrated in FIG. 4, the distancebetween the signal line 20 and the ground conductor 24 is substantiallyequal to the thickness T2 of the dielectric sheet 18 b, and, forexample, preferably is in the range of about 10 μm to about 100 μm, forexample. In this preferred embodiment, the distance between the signalline 20 and the ground conductor 24 preferably is about 50 μm, forexample. That is, design is performed so that the thickness T1 is largerthan the thickness T2.

Thus, by making the thickness T1 larger than the thickness T2, thecapacitance generated between the ground conductor 22 and the signalline 20 becomes small and the line width of the signal line 20 can beincreased so as to obtain a predetermined impedance (for example, about50Ω). As a result, a transmission loss can be reduced and the electricalcharacteristic of a high-frequency signal transmission line can beimproved. In this preferred embodiment, impedance design is performedmainly in consideration of the capacitance generated between the groundconductor 22 and the signal line 20. Impedance design for the groundconductor 24 is performed so as to significantly reduce and prevent theemission of a signal. That is, by setting a high characteristicimpedance (for example, about 70Ω) at the ground conductor 22 and thesignal line 20 and adding the ground conductor 24, a low-impedance (forexample, about 30Ω) area is provided at the high-frequency signaltransmission line. As a result, the impedance of the high-frequencysignal transmission line becomes a predetermined impedance (for example,about 50Ω).

The via-hole conductor b1 passes through the connection portion 18 a-bof the dielectric sheet 18 a in the z-axis direction, and connects theexternal terminal 16 a and the end of the signal line 20 in the negativex-axis direction. The via-hole conductor b2 passes through theconnection portion 18 a-c of the dielectric sheet 18 a in the z-axisdirection, and connects the external terminal 16 b and the end of thesignal line 20 in the positive x-axis direction. As a result, the signalline 20 is connected between the external terminals 16 a and 16 b. Thevia-hole conductors b1 and b2 are preferably made of a metal materialsuch as silver or copper having low resistivity, for example.

The via-hole conductors B1 pass through the line portion 18 a-a of thedielectric sheet 18 a in the z-axis direction, and are disposed at theline portion 18 a-a. The via-hole conductors B2 pass through the lineportion 18 b-a of the dielectric sheet 18 b in the z-axis direction, andare disposed at the line portion 18 b-a. The via-hole conductor B1 andthe via-hole conductor B2 are connected to each other, so that a singlevia-hole conductor is provided and connects the ground conductors 22 and24. The via-hole conductors B1 and B2 preferably are made of a metalmaterial such as silver or copper having low resistivity, for example.

The protection layer 14 covers the substantially entire surface of thedielectric sheet 18 a. As a result, the protection layer 14 covers theground conductor 22. For example, the protection layer 14 is made of aflexible resin such as a resist material.

As illustrated in FIG. 2, the protection layer 14 includes a lineportion 14 a and connection portions 14 b and 14 c. The line portion 14a covers the entire surface of the line portion 18 a-a, thereby coveringthe line portion 22 a.

The connection portion 14 b is connected to the end of the line portion14 a in the negative x-axis direction, and covers the surface of theconnection portion 18 a-b. At the connection portion 14 b, openings Hato Hd are provided. The opening Ha preferably is a rectangular orsubstantially rectangular opening located at the center of theconnection portion 14 b. The external terminal 16 a is exposed to theoutside via the opening Ha. The opening Hb preferably is a rectangularor substantially rectangular opening located in the positive y-axisdirection with respect to the opening Ha. The opening Hc preferably is arectangular or substantially rectangular opening arranged in thenegative x-axis direction with respect to the opening Ha. The opening Hdpreferably is a rectangular or substantially rectangular openingarranged in the negative y-axis direction with respect to the openingHa. The terminal portion 22 b is exposed to the outside via the openingsHb to Hd so as to define and function as an external terminal.

The connection portion 14 c is connected to the end of the line portion14 a in the positive x-axis direction, and covers the surface of theconnection portion 18 a-c. At the connection portion 14 c, openings Heto Hh are disposed. The opening He preferably is a rectangular orsubstantially rectangular opening located at the center of theconnection portion 14 c. The external terminal 16 b is exposed to theoutside via the opening He. The opening Hf preferably is a rectangularor substantially rectangular opening located in the positive y-axisdirection with respect to the opening He. The opening Hg preferably is arectangular or substantially rectangular opening located in the positivex-axis direction with respect to the opening He. The opening Hhpreferably is a rectangular or substantially rectangular opening locatedin the negative y-axis direction with respect to the opening He. Theterminal portion 22 c is exposed to the outside via the openings Hf toHh so as to define and function as an external terminal.

The connectors 100 a and 100 b are disposed on the surfaces of theconnection portions 12 b and 12 c, respectively. Since the structures ofthe connectors 100 a and 100 b are the same, the structure of theconnector 100 b will be described below by way of example.

As illustrated in FIGS. 1, 5A and 5B, the connector 100 b includes aconnector body 102, external terminals 104 and 106, a center conductor108, and external conductors 110. The connector body 102 preferably hasa shape obtained by coupling a cylinder with a rectangular orsubstantially rectangular plate and is made of an insulating materialsuch as a resin, for example.

The external terminal 104 is disposed on the surface of the plate of theconnector body 102 in the negative z-axis direction so that it faces theexternal terminal 16 b. The external terminals 106 are disposed on thesurface of the plate of the connector body 102 in the negative z-axisdirection so that the positions of the external terminals 106individually correspond to the positions of the openings Hf to Hhthrough which the terminal portion 22 c is exposed to the outside.

The center conductor 108 is disposed at the center of the cylinder ofthe connector body 102, and is connected to the external terminal 104.The center conductor 108 is a signal terminal arranged to receive oroutput a high-frequency signal. The external conductors 110 are disposedon the inner peripheral surface of the cylinder of the connector body102, and are connected to the external terminals 106. The externalconductors 110 are ground terminals holding the ground potential.

The connector 100 b having the above-described structure is disposed onthe surface of the connection portion 12 c so that the external terminal104 is connected to the external terminal 16 b and the externalterminals 106 are connected to the terminal portion 22 c. As a result,the signal line 20 is electrically connected to the center conductor108. The ground conductors 22 and 24 are electrically connected to theexternal conductors 110.

The high-frequency signal transmission line 10 is preferably used asdescribed below. FIGS. 6A and 6B are plan views of an electronicapparatus 200 including the high-frequency signal transmission line 10from the y-axis and z-axis directions. FIG. 7 is a cross-sectional viewof a portion C in FIG. 6A.

The electronic apparatus 200 preferably includes the high-frequencysignal transmission line 10, circuit boards 202 a and 202 b, receptacles204 a and 204 b, a battery pack (metal body) 206, and a casing 210.

At the circuit board 202 a, for example, a transmission circuit or areceiving circuit including an antenna is disposed. At the circuit board202 b, for example, a feeding circuit is disposed. The battery pack 206preferably is, for example, a lithium-ion secondary battery, and thesurface of the battery pack 206 is covered with a metal cover. Thecircuit board 202 a, the battery pack 206, and the circuit board 202 bare arranged in this order from the negative x-axis direction to thepositive x-axis direction.

The receptacles 204 a and 204 b are disposed on the main surfaces of thecircuit boards 202 a and 202 b in the negative z-axis direction,respectively. The connectors 100 a and 100 b are connected to thereceptacles 204 a and 204 b, respectively. As a result, a high-frequencysignal having the frequency of, for example, 2 GHz transmitted betweenthe circuit boards 202 a and 202 b is applied to the center conductors108 of the connectors 100 a and 100 b via the receptacles 204 a and 204b. The external conductors 110 of the connectors 100 a and 100 b areheld at the ground potential via the circuit boards 202 a and 202 b andthe receptacles 204 a and 204 b, respectively. As a result, thehigh-frequency signal transmission line 10 electrically and physicallyconnects the circuit boards 202 a and 202 b.

As illustrated in FIG. 7, the surface of the dielectric body 12 (moreaccurately, the surface of the protection layer 14) is in contact withthe battery pack 206. The surface of the dielectric body 12 and thebattery pack 206 are bonded to each other preferably with an adhesive,for example. The surface of the dielectric body 12 is a main surfacelocated on the side of the ground conductor 22 with respect to thesignal line 20. Accordingly, between the signal line 20 and the batterypack 206, there is the ground conductor 22 that is a solid conductor andthat continuously extends in the x-axis direction.

A non-limiting example of a manufacturing method of the high-frequencysignal transmission line 10 will be described below with reference toFIG. 2. An exemplary case in which a single high-frequency signaltransmission line 10 is created will be described. In reality, however,a plurality of high-frequency signal transmission lines 10 arepreferably manufactured at the same time by laminating large dielectricsheets and cutting the laminate.

First, the dielectric sheets 18 that are made of a thermoplastic resinand include copper foil on the entire surfaces thereof are prepared. Forexample, the surface of the copper foil on the dielectric sheet 18 issubjected to galvanization for rustproofing, thereby being smoothed. Thedielectric sheets 18 preferably have a thickness of about 20 μm to about80 μm and are preferably made of liquid crystal polymer, for example.The copper foil preferably has a thickness of about 10 μm to about 20μm, for example.

Subsequently, the external terminal 16 and the ground conductor 22illustrated in FIG. 2 are formed on the surface of the dielectric sheet18 a by photolithography. More specifically, a resist having the sameshape as each of the external terminal (16 a and 16 b) and the groundconductor 22 illustrated in FIG. 2 is printed on the copper foil on thedielectric sheet 18 a. A portion of the copper foil which is not coveredwith the resist is removed by etching the portion of the copper foil.Subsequently, the resist is removed. As a result, the external terminal16 and the ground conductor 22 illustrated in FIG. 2 are formed on thesurface of the dielectric sheet 18 a.

Subsequently, the signal line 20 illustrated in FIG. 2 is formed on thesurface of the dielectric sheet 18 b by photolithography. The groundconductor 24 illustrated in FIG. 2 is formed on the surface of thedielectric sheet 18 c by photolithography. These photolithographyprocesses are similar to the photolithography process of forming theexternal terminal 16 and the ground conductor 22, and the descriptionthereof will be omitted.

Subsequently, a laser beam is applied from the undersurfaces of thedielectric sheets 18 a and 18 b to positions at which the via-holeconductors b1, b2, B1, and B2 are to be formed, so that through holesare formed. Subsequently, a conductive paste is charged into the throughholes formed in the dielectric sheets 18 a and 18 b.

Subsequently, the dielectric sheets 18 a to 18 c are laminated in thisorder from the positive z-axis direction to the negative z-axisdirection so that the ground conductor 22, the signal line 20, and theground conductor 24 form a strip line structure. The dielectric sheets18 a to 18 c are softened, press-bonded, and integrated and theconductive paste charged into the through holes are solidified byapplying heat and pressure to the dielectric sheets 18 a to 18 c fromthe positive z-axis direction and the negative z-axis direction. As aresult, the via-hole conductors b1, b2, B1, and B2 illustrated in FIG. 2are formed. The dielectric sheets 18 are integrated by thermocompressionbonding in the above-described example, but may be integrated with anadhesive such as an epoxy resin. The via-hole conductors b1, b2, B1, andB2 may be formed by integrating the dielectric sheets 18, formingthrough holes in the dielectric sheets 18, and charging conductive pasteinto the through holes or forming a plating film in the through holes.

Finally, the protection layer 14 is formed on the dielectric sheet 18 aby applying a resin (resist) paste to the dielectric sheet 18 a.Consequently, the high-frequency signal transmission line 10 illustratedin FIG. 1 is obtained.

In the high-frequency signal transmission line 10 having theabove-described structure, a plurality of openings 30 are formed at theground conductor 24. Accordingly, the high-frequency signal transmissionline 10 can be easily bent.

With the high-frequency signal transmission line 10, the deviation ofthe characteristic impedance of the signal line from a predeterminedcharacteristic impedance (for example, about 50Ω) can be minimized. Morespecifically, in the flexible substrate disclosed in Japanese UnexaminedPatent Application Publication No. 2007-123740, an electromagnetic fieldmay exit from the opening portion of the flexible substrate. In a casewhere a dielectric or a metal body is disposed around the flexiblesubstrate, electromagnetic field coupling occurs between the signal linein the flexible substrate and the dielectric or the metal body. As aresult, the characteristic impedance of the signal line in the flexiblesubstrate may deviate from a predetermined characteristic impedance.

On the other hand, in the high-frequency signal transmission line 10,the surface of the dielectric body 12 on the side of the groundconductor 22 with respect to the signal line 20 is in contact with thebattery pack 206, and the surface of the dielectric body 12 on the sideof the ground conductor 24 is a noncontact surface apart from an article(a metal body) such as a battery pack. That is, between the signal line20 and the battery pack 206, the ground conductor 24 at which theopenings 30 are provided are not present but the ground conductor 22 atwhich substantially no opening is provided is present. As a result, theoccurrence of electromagnetic field coupling between the signal line 20and the battery pack 206 is prevented. In the high-frequency signaltransmission line 10, the deviation of the characteristic impedance ofthe signal line 20 from a predetermined characteristic impedance istherefore minimized. That is, even in a case where the clearance (space)between a mounted component and an electronic component in the casing ofan electronic apparatus such as a communication terminal is narrow orthe clearance (space) between the casing and each of these components isnarrow, the high-frequency signal transmission line 10 can be disposedin the space so that the surface of the high-frequency signaltransmission line 10 on the side of the ground conductor 22 is incontact with an article (a metal body). Accordingly, it is possible toreduce a characteristic change caused by the positional change of ahigh-frequency signal transmission line and obtain a high-frequencysignal transmission line that is unaffected by the electronic componentand the casing. In particular, in a case where a high-frequency signaltransmission line is bonded to an article (a metal body) with anadhesive like the high-frequency signal transmission line 10, thecharacteristic change caused by the positional change can be reducedwith more certainty.

For the following other reasons, the high-frequency signal transmissionline 10 can be easily bent. A characteristic impedance Z of thehigh-frequency signal transmission line 10 is represented by √(L/C)where L denotes an inductance value per unit length of thehigh-frequency signal transmission line 10 and C denotes a capacitancevalue per unit length of the high-frequency signal transmission line.The high-frequency signal transmission line 10 is designed so that Zbecomes a predetermined characteristic impedance (for example, about50Ω).

As a method of allowing the high-frequency signal transmission line 10to be easily bent, a method of reducing the thickness of thehigh-frequency signal transmission line 10 in the z-axis direction(hereinafter merely referred to as a thickness) is considered. However,in a case where the thickness of the high-frequency signal transmissionline 10 is reduced, the distance between the signal line 20 and each ofthe ground conductors 22 and 24 is reduced and the capacitance value Cis increased. As a result, the characteristic impedance Z becomessmaller than the predetermined characteristic impedance.

Another method is considered for reducing the line width of the signalline 20 in the y-axis direction (hereinafter merely referred to as aline width) so as to increase the inductance value L of the signal line20 and for reducing the area of the signal line 20 facing the groundconductors 22 and 24 so as to reduce the capacitance value C.

However, it is difficult to precisely form the signal line 20 having asmall line width. In addition, the reduction in the line width of thesignal line 20 increases a transmission loss and deteriorates anelectrical characteristic.

Accordingly, in the high-frequency signal transmission line 10, theopenings 30 are provided at the ground conductor 24. The area of thesignal line 20 facing the ground conductor 24 is therefore reduced andthe capacitance value C becomes smaller. As a result, it is possible toeasily bend the high-frequency signal transmission line 10 whilemaintaining the characteristic impedance Z at a predeterminedcharacteristic impedance.

In the high-frequency signal transmission line 10, the ground conductor24 is disposed between the dielectric sheets 18 b and 18 c. The groundconductor 24 is not therefore exposed to the outside on the undersurfaceof the dielectric body 12. Accordingly, even in a case where anotherarticle is disposed on the undersurface of the dielectric body 12, theground conductor 24 and the article do not directly face each other.This leads to the reduction in the change of the characteristicimpedance of the signal line 20.

A non-limiting example of an installation method according to a firstmodification of a preferred embodiment of the present invention will bedescribed below. FIG. 8 is a cross-sectional view of the high-frequencysignal transmission line 10 and the battery pack 206 to which thehigh-frequency signal transmission line 10 is fixed with an installationmethod according to the first preferred embodiment.

In a case where an installation method according to the firstmodification is used, the ground conductor 22 is electrically connectedto the battery pack 206. More specifically, openings Op are provided atthe protection layer 14. The ground conductor 22 is partly exposed tothe outside via the openings Op provided at the protection layer 14.Solder or a conductive adhesive is charged into the openings Op, so thatconnection conductors 212 are formed. As a result, the ground conductor24 is electrically connected to and fixed to the battery pack 206.

In the high-frequency signal transmission line 10 that has beeninstalled with the above-described installation method, the groundconductors 22 and 24 are maintained at the ground potential not only viathe terminal portions 22 b and 22 c but also via the battery pack 206that is a metal article. Accordingly, the ground conductors 22 and 24are more stably maintained at the ground potential. The metal article isnot limited to a battery pack, and may be a printed circuit board (forexample, a ground terminal) or a metal casing.

Next, a non-limiting example of an installation method according to asecond modification of a preferred embodiment of the present inventionwill be described. FIG. 9 is a cross-sectional view of thehigh-frequency signal transmission line 10 and the battery pack 206 towhich the high-frequency signal transmission line 10 is fixed with aninstallation method according to the second preferred embodiment.

With an installation method according to the second modification, thehigh-frequency signal transmission line 10 is bent along the surface ofthe battery pack 206 and is attached to the battery pack 206. Since thehigh-frequency signal transmission line 10 can be easily deformed, itcan be bent along the battery pack 206.

Next, a non-limiting example of an installation method according to athird modification of a preferred embodiment of the present inventionwill be described below. FIG. 10 is an external perspective view of theinside of the electronic apparatus 200 in a case where an installationmethod according to the third modification is used.

The high-frequency signal transmission line 10 illustrated in FIGS. 6Aand 6B extends in the x-axis direction on the surface of the batterypack 206 in the negative z-axis direction without being bent.

On the other hand, the connection portions 12 b and 12 c of thehigh-frequency signal transmission line 10 illustrated in FIG. 10 arebent with respect to the line portion 12 a. As a result, thehigh-frequency signal transmission line 10 extends in the x-axisdirection on the side surface of the battery pack 206 in the positivey-axis direction. Since the high-frequency signal transmission line 10can be easily bent, such arrangement can be easily achieved.

The structure of a high-frequency signal transmission line according tothe first modification of a preferred embodiment of the presentinvention will be described below with reference to the accompanyingdrawings. FIG. 11 is an exploded view of a laminate 12 in ahigh-frequency signal transmission line 10 a according to the firstmodification. FIG. 12 is a perspective view of the high-frequency signaltransmission line 10 a illustrated in FIG. 11 from the z-axis direction.FIG. 13 is an equivalent circuit diagram of a portion of thehigh-frequency signal transmission line 10 a according to the firstmodification.

The difference between the high-frequency signal transmission lines 10and 10 a is the shape of the openings 30. The structure of thehigh-frequency signal transmission line 10 a will be described below,focusing on the difference.

The ground conductor 24 preferably has a ladder shape obtained byalternately disposing a plurality of openings 30 and a plurality ofbridge portions 60 along the signal line 20. As illustrated in FIG. 12,the openings 30 overlap the signal line 20 in plan view from the z-axisdirection, and are symmetric with respect to the signal line 20. Thatis, the signal line 20 traverses the midsections of the openings 30 inthe y-axis direction.

In addition, each of the openings 30 is symmetric with respect to a lineA that passes through the midsection of the opening 30 in a direction(the x-axis direction) in which the signal line 20 extends and isperpendicular or substantially perpendicular to the signal line 20 (thatis, the line A extends in the y-axis direction). Detailed descriptionwill be provided below.

A region including the midsection of the opening 30 in the x-axisdirection is defined as a region A1. A region corresponding to thebridge portion 60 is defined as a region A2. A region between theregions A1 and A2 is defined as a region A3. The region A3 is located oneither side of the region A1 in the x-axis direction, and is adjacent tothe regions A1 and A2. For example, the length of the region A2 in thex-axis direction (that is, the length of the bridge portion 60) ispreferably in the range of about 25 μm to about 200 μm. In thispreferred embodiment, the length of the region A2 in the x-axisdirection preferably is about 100 μm, for example.

As illustrated in FIG. 12, the line A passes through the midsection ofthe region A1 in the x-axis direction. A width W1 of the opening 30 inthe region A1 in a direction (the y-axis direction) perpendicular orsubstantially perpendicular to the signal line 20 is larger than a widthW2 of the opening 30 in the region A3 in the y-axis direction. That is,the width of the opening 30 at the midsection thereof in the x-axisdirection is larger than that of the other portion of the opening 30,and the opening 30 is symmetric with respect to the line A. The regionA1 is a region in which the opening 30 has the width W1 in the y-axisdirection, and the region A3 is a region in which the opening 30 has thewidth W2 in the y-axis direction. Accordingly, there is a step betweenthe regions A1 and A3 of the opening 30. For example, the width W1 ispreferably in the range of about 500 μm to about 1500 μm. In thispreferred embodiment, the width W1 preferably is about 900 μm, forexample. For example, the width W2 preferably is in the range of about250 μm to about 750 μm. In this preferred embodiment, the width W2preferably is about 480 μm, for example.

For example, a length G1 of the openings 30 in the x-axis directionpreferably is in the range of about 1 mm to about 5 mm. In thispreferred embodiment, the length G1 preferably is about 3 mm, forexample. The length G1 is larger than the width W1 that is the maximumwidth of the openings 30. It is desired that the length G1 be abouttwice the width W1 or longer, for example.

At the ground conductor 24, no opening is provided between adjacent onesof the openings 30. More specifically, in the region A2 sandwichedbetween adjacent ones of the openings 30, a conductive layer (the bridgeportion 60) uniformly extends and no opening is present.

In the high-frequency signal transmission line 10 a having theabove-described structure, the characteristic impedance of the signalline 20 changes such that, with increasing proximity to the other one oftwo adjacent bridge portions 60 from one of them, the characteristicimpedance increases in the order of a minimum value Z2, an intermediatevalue Z3, and a maximum value Z1 and then decreases in the order of themaximum value Z1, the intermediate value Z3, and the minimum value Z2.More specifically, the opening 30 has the width W1 in the region A1 andthe width W2 smaller than the width W1 in the region A3. Accordingly,the distance between the signal line 20 and the ground conductor 24 inthe region A1 is larger than that in the region A3. As a result, theintensity of a magnetic field generated at the signal line 20 in theregion A1 is higher than that of a magnetic field generated at thesignal line 20 in the region A3, and an inductance component at theregion A1 is increased. That is, in the region A1, an inductivecomponent becomes dominant.

In the regions A2, the bridge portions 60 are provided. Accordingly, thedistance between the signal line 20 and the ground conductor 24 in theregion A3 is larger than that in the region A2. As a result, acapacitance generated at the signal line 20 in the region A2 is largerthan that generated at the signal line 20 in the region A3, and theintensity of a magnetic field generated in the region A2 is lower thanthat of a magnetic field generated in the region A3. That is, in theregion A2, a capacitive component becomes dominant.

Consequently, in the region A1, the characteristic impedance of thesignal line 20 becomes the maximum value Z1. That is, at a position atwhich the characteristic impedance of the signal line 20 is the maximumvalue Z1, the opening 30 has the width W1. In the region A3, thecharacteristic impedance of the signal line 20 becomes the intermediatevalue Z3. That is, at a position at which the characteristic impedanceof the signal line 20 is the intermediate value Z3, the opening 30 hasthe width W2. In the region A2, the characteristic impedance of thesignal line 20 becomes the minimum value Z2.

The high-frequency signal transmission line 10 therefore has a circuitconfiguration illustrated in FIG. 13. More specifically, in the regionA1, since substantially no capacitance is generated between the signalline 20 and the ground conductor 24, the characteristic impedance Z1 isgenerated mainly by the inductance L1 of the signal line 20. In theregion A2, since a large capacitance C3 is generated between the signalline 20 and the ground conductor 24, the characteristic impedance Z2 isgenerated mainly by the capacitance C3. In the region A3, since acapacitance C2 smaller than the capacitance C3 is generated between thesignal line 20 and the ground conductor 24, the characteristic impedanceZ3 is generated by an inductance L2 of the signal line 20 and thecapacitance C2. The characteristic impedance Z3 preferably is, forexample, about 55Ω. The characteristic impedance Z1 is higher than thecharacteristic impedance Z3, and preferably is, for example, about 70Ω.The characteristic impedance Z2 is lower than the characteristicimpedance Z3, and preferably is, for example, about 30Ω. The overallcharacteristic impedance of the high-frequency signal transmission line10 preferably is about 50Ω, for example.

In the high-frequency signal transmission line 10 a, the characteristicimpedance of the signal line 20 changes such that, with increasingproximity to the other one of two adjacent bridge portions 60 from oneof them, the characteristic impedance increases in the order of theminimum value Z2, the intermediate value Z3, and the maximum value Z1and then decreases in the order of the maximum value Z1, theintermediate value Z3, and the minimum value Z2. Accordingly, theelectrode width of the signal line 20 can be increased while reducingthe profile of the high-frequency signal transmission line 10 a. As aresult, the surface area of electrode portions of the signal line 20 andthe ground conductors 22 and 24 through which a high-frequency currentflows can be increased and the transmission loss of a high-frequencysignal is reduced. As illustrated in FIG. 12, since a length ALcorresponding to one cycle (the region A1, the two regions A2, and theregions A3) preferably is a short length that falls within the range ofabout 1 mm to about 5 mm, the suppression of unnecessary radiation andthe reduction in the transmission loss can be realized even in ahigher-frequency range. Since the region A3 is placed on either side ofthe region A1, a strong magnetic field generated by a current passingthrough the signal line 20 is not directly transmitted to the region A2.As a result, the ground potential of the region A2 becomes stable and aneffect of shielding by the ground conductor 24 is obtained. This leadsto the significant reduction and prevention of unnecessary radiation.Consequently, in the high-frequency signal transmission line 10 a, evenin a case where the distance between the signal line 20 and each of theground conductors 22 and 24 is reduced, the line width of the signalline 20 can be increased. It is therefore possible to reduce the profileof the high-frequency signal transmission line 10 a and realize thereduction in the transmission loss and the significant reduction andprevention of unnecessary radiation while keeping the characteristicimpedance of the high-frequency signal transmission line 10 a. Thehigh-frequency signal transmission line 10 a can be therefore easilybent, and can be used after being bent.

In the high-frequency signal transmission line 10 a, since the groundpotential of the ground conductor 24 becomes stable, a transmission losscan be reduced. In addition, a shielding characteristic can be improved.More specifically, in the high-frequency signal transmission line 10 a,the width W1 of the opening 30 in the region A1 is larger than the widthW2 of the opening 30 in the region A3. Accordingly, in thehigh-frequency signal transmission line 10 a, the magnetic energy of thesignal line 20 in the region A1 is larger than that in the region A3.The magnetic energy of the signal line 20 in the region A2 is smallerthan that in the region A3. The characteristic impedance of the signalline 20 is repeatedly changed in the order of Z2, Z3, Z1, Z3, Z2 . . . .The change in magnetic energy at adjacent portions of the signal line 20in the x-axis direction is therefore slow. As a result, at the boundarybetween structural units (the regions A1 to A3), magnetic energy becomessmall, the change in the ground potential of a ground conductor isreduced, and the significant reduction and prevention of unnecessaryradiation and the reduction in the transmission loss of a high-frequencysignal are realized. That is, the region A3 can significantly reduce andprevent the generation of an unnecessary inductance component at thebridge portion 60. As a result, the mutual inductance componentgenerated between the bridge portion 60 and the signal line 20 can bereduced and the ground potential can be stable. Thus, even in thelow-profile high-frequency signal transmission line in which therelatively large openings 30 are provided at the ground conductor,unnecessary radiation can be significantly reduced and prevented and thetransmission loss of a high-frequency signal can be reduced.

Since the via-hole conductors B1 are disposed in a direction in whichthe bridge portions 60 extend, the generation of an unnecessaryinductance component at the bridge portions 60 can be significantlyreduced and prevented. In particular, since the length G1 of the opening30 in the x-axis direction (that is the distance between the bridgeportions 60) is larger than the width W1 of the opening 30 in the regionA1, the area of the opening 30 can be maximized. As a result, theoccurrence of unnecessary radiation can be significantly reduced andprevented while obtaining a predetermined characteristic impedance.

The openings 30 are structural units disposed at regular intervals in adirection (the x-axis direction) in which the signal line 20 extends.Accordingly, the frequency characteristic of the characteristicimpedance of the signal line 20 in the openings 30 can be determined inaccordance with the length of the openings 30 in the x-axis direction.That is, as the length G1 of the openings 30 is reduced, the frequencycharacteristic of the characteristic impedance of the signal line can beextended to a higher-frequency range. With the increasing length G1 ofthe openings 30, the width W1 of the openings 30 in the region A1 can bereduced and the openings 30 can extend in a narrow strip form. Since theoccurrence of unnecessary radiation can be significantly reduced andprevented and a transmission loss can be reduced, the stable impedancecharacteristic of the high-frequency signal transmission line 10 a in abroader band can be achieved.

The high-frequency signal transmission line 10 a can be used after beingbent for the following reason. In the region A1, since the width of theopenings 30 in the y-axis direction is the largest, the high-frequencysignal transmission line 10 is most susceptible to bending. On the otherhand, in the region A2, since no opening 30 is provided, it is hardlybent. In a case where the high-frequency signal transmission line 10 ais used after being bent, it is bent in the region A1 and is hardly bentin the region A2. In the high-frequency signal transmission line 10 a,the via-hole conductors B1 and B2, which are less deformable than thedielectric sheets 18, are therefore disposed in the region A2. As aresult, the high-frequency signal transmission line 10 a can be easilybent in the region A1.

In the high-frequency signal transmission line 10 a, a predeterminedcharacteristic impedance can also be obtained by adjusting the distanceT1 between the signal line 20 and the ground conductor 22 and thedistance T2 between the signal line 20 and the ground conductor 24.

In the high-frequency signal transmission line 10 a, the length G1 ofthe openings 30 in a direction in which the signal line 20 extends islarger than the width W1 for the following reason. More specifically, ahigh-frequency signal transmission mode in the high-frequency signaltransmission line 10 is a TEM mode. In the TEM mode, an electric fieldand a magnetic field are generated in a direction perpendicular orsubstantially perpendicular to a high-frequency signal transmissiondirection (the x-axis direction). That is, a magnetic field is generatedin the form of circles around the signal line 20, and an electric fieldradially extends from the signal line 20 to the ground conductors 22 and24. The magnetic field, which forms circles, is only deformed at theopenings 30 provided at the ground conductor 22 so that the radii of thecircles become larger. Accordingly, the magnetic field does notsignificantly leak from the high-frequency signal transmission line 10a. On the other hand, the electric field is partly emitted from thehigh-frequency signal transmission line 10 a. Accordingly, the radiationof an electric field occupies a large portion of unnecessary radiationin the high-frequency signal transmission line 10 a.

Since the electric field is perpendicular or substantially perpendicularto a high-frequency signal transmission direction (the x-axisdirection), the increase in the width W1 of the opening 30 in the y-axisdirection increases the amount of electric field emitted from theopening 30 (the amount of unnecessary radiation). On the other hand, thelarger the width W1, the higher the characteristic impedance of thehigh-frequency signal transmission line 10 a. However, since there is noelectric field at a distance of approximately three times the line widthof the signal line 20 from the signal line 20 in a directionperpendicular or substantially perpendicular to the high-frequencysignal transmission direction (x-axis direction) in the high-frequencysignal transmission line 10 a, the further increase in the width W1cannot increase the characteristic impedance. Accordingly, excessiveincrease in the width W1 is undesirable in consideration of the factthat the amount of unnecessary radiation is increased as the width W1increases. In addition, in a case where the width W1 reachesapproximately half the wavelength of a high-frequency signal, a slotantenna is formed, an electromagnetic wave is emitted, and the amount ofunnecessary radiation is increased.

On the other hand, the longer the length G1 of the opening 30 in thex-axis direction, the smaller the area of the signal line 20 facing theground conductor 22. Accordingly, the line width of the signal line 20can be increased. As a result, the high-frequency resistance value ofthe signal line 20 can be reduced.

In a case where the length G1 is larger than the width W1, thehigh-frequency resistance value of a counter current (eddy current) inthe ground conductor 22 is small.

It is therefore desired that the length G1 be larger than the width W1,and, be preferably twice the width W1 or longer. At that time, inconsideration of the fact that a slot antenna is formed and anelectromagnetic wave is emitted from the opening 30 in a case where thelength G1 of the opening 30 in the x-axis direction reachesapproximately half the wavelength of a high-frequency signal, the lengthG1 is preferably much shorter than the wavelength.

A high-frequency signal transmission line according to the secondmodification of a preferred embodiment of the present invention will bedescribed below with reference to the accompanying drawing. FIG. 14 isan exploded view of the laminate 12 in a high-frequency signaltransmission line 10 b according to the second modification.

The difference between the high-frequency signal transmission lines 10 band 10 a is the shape of the openings 30. More specifically, asillustrated in FIG. 11, the width of the openings 30 of thehigh-frequency signal transmission line 10 a in the y-axis direction isdiscontinuously changed in a stepwise manner. In contrast, the width ofthe openings 30 of the high-frequency signal transmission line 10 b inthe y-axis direction is continuously changed. More specifically, thewidth of the opening 30 in the y-axis direction is continuously reducedas the distance from the center of the opening 30 in the x-axisdirection increases. As a result, the magnetic energy and characteristicimpedance of the signal line 20 are continuously changed.

As illustrated in FIG. 14, in the high-frequency signal transmissionline 10 b, the region A1 has the line A as the center line and includesa portion of the opening 30 having the width W1 in the y-axis direction.Accordingly, in the region A1, the characteristic impedance of thesignal line 20 becomes the maximum value Z1. The region A2 is providedbetween the openings and includes the bridge portion 60. Accordingly, inthe region A2, the characteristic impedance of the signal line 20becomes the minimum value Z2. The region A3 is sandwiched between theregions A1 and A2, and includes a portion of the opening 30 having thewidth W2 in the y-axis direction. Accordingly, in the region A3, thecharacteristic impedance of the signal line 20 becomes the intermediatevalue Z3.

The region A1 needs to include only the portion of the opening 30 havingthe width W1 in the y-axis direction, and the region A3 needs to includeonly the portion of the opening 30 having the width W2 in the y-axisdirection. Accordingly, in the present preferred embodiment, theboundary between the regions A1 and A3 is not clearly defined. Forexample, the boundary between the regions A1 and A3 is a position atwhich the width of the opening 30 in the y-axis direction is (W1+W2)/2.

Like the high-frequency signal transmission line 10, the high-frequencysignal transmission line 10 b having the above-described structure canbe used after being bent, can significantly reduce and prevent theoccurrence of unnecessary radiation, and can significantly reduce andprevent a transmission loss in the signal line 20.

A high-frequency signal transmission line according to the thirdmodification of a preferred embodiment of the present invention will bedescribed below with reference to the accompanying drawing. FIG. 15 isan exploded view of the laminate 12 in a high-frequency signaltransmission line 10 c according to the third modification.

The difference between the high-frequency signal transmission lines 10 cand 10 a is the presence of ground conductors 40 and 42. Morespecifically, in the high-frequency signal transmission line 10 c, theground conductors 40 and 42 are disposed on the surface of thedielectric sheet 18 b. The ground conductor 40 preferably is arectangular or substantially rectangular conductor that is present inthe positive y-axis direction with respect to the signal line 20 andextends in the x-axis direction. The ground conductor 40 is connected tothe ground conductors 22 and 24 via the via-hole conductors B1 and B2,respectively. The ground conductor 42 preferably is a rectangular orsubstantially rectangular conductor that is present in the negativey-axis direction with respect to the signal line 20 and extends in thex-axis direction. The ground conductor 42 is connected to the groundconductors 22 and 24 via the via-hole conductors B1 and B2,respectively.

In the high-frequency signal transmission line 10 c, since the groundconductors 40 and 42 are individually disposed on both sides of thesignal line 20 in the y-axis direction, the occurrence of unnecessaryradiation from the signal line 20 to both sides of the signal line 20 inthe y-axis direction is significantly reduced and prevented.

A high-frequency signal transmission line according to the fourthmodification of a preferred embodiment of the present invention will bedescribed below with reference to the accompanying drawing. FIG. 16 isan exploded view of the laminate 12 in a high-frequency signaltransmission line 10 d according to the fourth modification.

The difference between the high-frequency signal transmission lines 10 dand 10 a is the shape of openings (the openings 30 and openings 44 a and44 b). More specifically, the openings 44 a and 44 b are obtained bydividing the opening 30 into two portions in the positive y-axisdirection and the negative y-axis direction. In the high-frequencysignal transmission line 10 d, a linear conductor 46 extending in thex-axis direction is disposed between the openings 44 a and 44 b. Thelinear conductor is a portion of the ground conductor 24 and overlapsthe signal line 20 in plan view from the z-axis direction.

In the high-frequency signal transmission line 10 d, a plurality ofopenings 44 a are arranged along the signal line 20, and a plurality ofopenings 44 b are arranged along the signal line 20. As a result, in theregion A1, the characteristic impedance of the signal line 20 becomesthe maximum value Z1. In the region A3, the characteristic impedance ofthe signal line 20 becomes the intermediate value Z3. In the region A2,the characteristic impedance of the signal line 20 becomes the minimumvalue Z2.

In the high-frequency signal transmission line 10 d, as illustrated inFIG. 16, the line width of the linear conductor 46 is smaller than thatof the signal line 20. Accordingly, the signal line 20 protrudes fromthe linear conductor 46 in plan view from the z-axis direction. The linewidth of the linear conductor 46 may be larger than that of the signalline 20, and the signal line 20 does not necessarily have to protrudefrom the linear conductor 46. That is, the openings 44 a and 44 b do notnecessarily have to overlap the signal line 20. Similarly, the openings30 do not necessarily have to overlap the signal line 20. In thehigh-frequency signal transmission line 10 d, the direction ofhigh-frequency currents flowing through the linear conductor 46 and theground conductors 22 and 24 is opposite to that of a high-frequencycurrent flowing through the signal line 20. Accordingly, even in a casewhere the signal line 20 protrudes from the linear conductor 46, thehigh-frequency signal transmission line 10 d can more effectively reduceand prevent the occurrence of unnecessary radiation as compared with thehigh-frequency signal transmission line 10.

A high-frequency signal transmission line according to the sixthmodification of a preferred embodiment of the present invention will bedescribed below with reference to the accompanying drawings. FIG. 17 isan exploded view of the laminate 12 in a high-frequency signaltransmission line 10 e according to the fifth modification. FIG. 18 is aperspective view of the high-frequency signal transmission line 10 eillustrated in FIG. 17 from the z-axis direction.

A first difference between the high-frequency signal transmission lines10 e and 10 a is that the line width of the signal line 20 at the bridgeportions 60 is smaller than that of the signal line 20 at positions atwhich the characteristic impedance of the signal line 20 becomes themaximum value Z1. A second difference between the high-frequency signaltransmission lines 10 e and 10 a is that the opening 30 tapers between aposition at which the characteristic impedance of the signal line 20becomes the intermediate value Z3 (that is, the position at which thewidth W2 of the opening 30 in the y-axis direction is obtained) and aposition at which the characteristic impedance of the signal line 20becomes the maximum value Z1 (that is, the position at which the widthW1 of the opening 30 in the y-axis direction is obtained). A thirddifference between the high-frequency signal transmission lines 10 e and10 a is that the opening 30 tapers between a position at which thecharacteristic impedance of the signal line 20 becomes the intermediatevalue Z3 (that is, the position at which the width W2 of the opening 30in the y-axis direction is obtained) and the bridge portion 60.

First, the definitions of the regions A1 to A3 in the high-frequencysignal transmission line 10 e will be described with reference to FIG.18. The region A1 is a region in which the width W1 of the opening 30 inthe y-axis direction is obtained. The region A2 is a regioncorresponding to the bridge portion 60. The region A3 is sandwichedbetween the regions A1 and A2, and includes a portion of the opening 30having the width W2 in the y-axis direction.

The first difference will be described. As illustrated in FIGS. 17 and18, the signal line 20 has a line width Wb in the region A2. The signalline 20 has a line width Wa larger than the line width Wb in the regionA1. For example, the line width Wa is preferably in the range of about100 μm to about 500 μm. In the present preferred embodiment, the linewidth Wa preferably is about 350 μm, for example. For example, the linewidth Wb preferably is in the range of about 25 μm to about 250 μm, forexample. In the present preferred embodiment, the line width Wbpreferably is about 100 μm, for example. Since the line width of thesignal line 20 in the region A2 is smaller than that in the region A1,the area of a portion of the signal line 20 overlapping the bridgeportion 60 is reduced. As a result, a stray capacitance generatedbetween the signal line 20 and the bridge portion 60 is reduced.Furthermore, since a portion of the signal line 20 overlapping theopening 30 has the line width Wa, the increase in the inductance valueof the portion of the signal line 20 can be significantly reduced andprevented. Still furthermore, since the line width of the signal line 20is not wholly narrowed but partly narrowed, the increase in theresistance value of the signal line 20 is significantly reduced andprevented.

The signal line 20 tapers with the change in the line width thereof. Asa result, at a portion of the signal line 20 whose line width varies,the change in a resistance value becomes slow and the occurrence of thereflection of a high-frequency signal is significantly reduced andprevented.

The second difference will be described. The opening tapers between theposition at which the width W2 of the opening 30 in the y-axis directionis obtained and the position at which the width W1 of the opening 30 inthe y-axis direction is obtained. That is, the end portion of the regionA3 in the x-axis direction tapers. As a result, the loss of a currentpassing through the ground conductor 24 is reduced.

The third difference will be described. The opening 30 tapers betweenthe position at which the width W2 of the opening 30 in the y-axisdirection is obtained and the bridge portion 60. That is, both endportions of the bridge portion 60 in the y-axis direction taper. Aportion of the bridge portion 60 overlapping the signal line 20therefore has a line width smaller than that of the other portion of thebridge portion 60 in the x-axis direction. As a result, a straycapacitance generated between the bridge portion 60 and the signal line20 is reduced. Since the line width of the bridge portion 60 is notwholly narrowed but partly narrowed, the increases in the resistancevalue and inductance value of the bridge portion 60 are significantlyreduced and prevented.

A high-frequency signal transmission line according to the sixthmodification of a preferred embodiment of the present invention will bedescribed below with reference to the accompanying drawings. FIG. 19 isan exploded view of the laminate 12 in a high-frequency signaltransmission line 10 f according to the sixth modification. FIG. 20 is aperspective view of the high-frequency signal transmission line 10 fillustrated in FIG. 19 from the z-axis direction.

The difference between the high-frequency signal transmission lines 10 fand 10 a is that a floating conductor 50 is disposed. More specifically,the high-frequency signal transmission line 10 f further includes adielectric sheet 18 d and the floating conductor 50. The dielectricsheet 18 d is located on the surface of the dielectric sheet 18 c in thenegative z-axis direction.

As illustrated in FIGS. 19 and 20, the floating conductor 50 preferablyis a rectangular or substantially rectangular conductive layer and isdisposed on the surface of the dielectric sheet 18 d. The floatingconductor 50 is located on the opposite side of the ground conductor 24respect to the signal line 20.

The floating conductor 50 faces the signal line 20 and the groundconductor 24 in plan view from the z-axis direction. A width W3 of thefloating conductor 50 in the y-axis direction is smaller than the widthW1 of the opening 30 in the region A1 and is larger than the width W2 ofthe opening 30 in the region A3. The bridge portions 60 are covered withthe floating conductor 50.

The floating conductor 50 is not electrically connected to conductivelayers such as the signal line 20 and the ground conductor 24, andprovides a floating potential. The floating potential is a potentialbetween the signal line 20 and the ground conductor 24.

In the high-frequency signal transmission line 10 f in which thefloating conductor 50 faces the signal line 20, even in a case where astray capacitance is generated between the signal line 20 and thefloating conductor 50, the characteristic impedance of the signal line20 is hardly changed. More specifically, since the floating conductor 50is not electrically connected to the signal line 20 and the groundconductors 22 and 24, the floating conductor 50 provides a floatingpotential. Accordingly, the stray capacitance between the signal line 20and the floating conductor 50 and the stray capacitance between thefloating conductor 50 and the ground conductor 24 are serially connectedto each other.

The width W3 of the floating conductor 50 is smaller than the width W1of the opening 30 in the region A1 and is larger than the width W2 ofthe opening 30 in the region A3. Accordingly, the area of a portion ofthe floating conductor 50 facing the ground conductor 24 is small, andthe stray capacitance between the ground conductor 24 and the floatingconductor 50 is also small. A capacitance obtained by combining thestray capacitance between the signal line 20 and the floating conductor50 and the stray capacitance between the floating conductor 50 and theground conductor 24, which are serially connected to each other, istherefore small. With the floating conductor 50, the amount of change inthe characteristic impedance of the signal line 20 becomes small.

Second Preferred Embodiment

A high-frequency signal transmission line and an electronic apparatusaccording to the second preferred embodiment of the present inventionwill be described below with reference to the accompanying drawings.

The structure of a high-frequency signal transmission line according tothe second preferred embodiment of the present invention will bedescribed below with reference to the accompanying drawings. FIG. 21 isan external perspective view of a high-frequency signal transmissionline 10 g according to the second preferred embodiment of the presentinvention. FIG. 22 is an exploded view of the dielectric body 12 in thehigh-frequency signal transmission line 10 g illustrated in FIG. 21.FIG. 23 is a cross-sectional view of the high-frequency signaltransmission line 10 g illustrated in FIG. 21. FIG. 24 is across-sectional view of the high-frequency signal transmission line 10g. Referring to FIGS. 21 to 24, a lamination direction in thehigh-frequency signal transmission line 10 g is defined as a z-axisdirection, a longitudinal direction in the high-frequency signaltransmission line 10 g is defined as an x-axis direction, and adirection orthogonal to the x-axis direction and the z-axis direction isdefined as a y-axis direction.

For example, the high-frequency signal transmission line 10 g ispreferably used to connect two high-frequency circuits in an electronicapparatus such as a mobile telephone. As illustrated in FIGS. 21 to 23,the high-frequency signal transmission line 10 g includes the dielectricbody 12, the external terminal 16 (16 a and 16 b), the signal line 20,the ground conductors 22 and 24, an adhesive layer 70, a cover sheet 72,the via-hole conductors b1, b2, B1, and B2, and the connectors 100 a and100 b.

As illustrated in FIG. 21, the dielectric body 12 extends in the x-axisdirection in plan view from the z-axis direction, and includes the lineportion 12 a and the connection portions 12 b and 12 c. The dielectricbody 12 is a laminate obtained by laminating the protection layer 14 andthe dielectric sheets (insulating layers) 18 (18 a to 18 c), which areillustrated in FIG. 22, in this order from the positive z-axis directionto the negative z-axis direction. The dielectric body 12 hasflexibility, and includes two main surfaces. In the followingdescription, the main surface of the dielectric body 12 in the positivez-axis direction is referred to as a surface (the first main surface)and the main surface of the dielectric body 12 in the negative z-axisdirection is referred to as an undersurface (the second main surface).

The line portion 12 a extends in the x-axis direction. The connectionportion 12 b is connected to the end of the line portion 12 a in thenegative x-axis direction, and the connection portion 12 c is connectedto the end of the line portion 12 a in the positive x-axis direction.The connection portions 12 b and 12 c preferably are rectangular orsubstantially rectangular in shape. The width of the connection portions12 b and 12 c in the y-axis direction is larger than that of the lineportion 12 a in the y-axis direction.

The dielectric sheet 18 extends in the x-axis direction in plan viewfrom the z-axis direction, and is an insulating layer having the sameshape as the dielectric body 12. The dielectric sheet 18 is made of athermoplastic resin such as polyimide or liquid crystal polymer havingflexibility. As illustrated in FIG. 24, the thickness T1 of thedielectric sheet 18 a is larger than the thickness T2 of the dielectricsheet 18 b. For example, after the dielectric sheets 18 a to 18 c havebeen laminated, the thickness T1 preferably is in the range of about 50μm to about 300 μm, for example. In the present preferred embodiment,the thickness T1 preferably is about 150 μm, for example. The thicknessT2 is preferably in the range of about 10 μm to about 100 μm, forexample. In the present preferred embodiment, the thickness T2preferably is about 50 μm, for example. In the following description,the main surface of the dielectric sheet 18 in the positive z-axisdirection is referred to as a surface, and the main surface of thedielectric sheet 18 in the negative z-axis direction is referred to asan undersurface.

The dielectric sheet 18 a includes the line portion 18 a-a and theconnection portions 18 a-b and 18 a-c. The dielectric sheet 18 bincludes the line portion 18 b-a and the connection portions 18 b-b and18 b-c. The dielectric sheet 18 c includes the line portion 18 c-a andthe connection portions 18 c-b and 18 c-c. The line portions 18 a-a, 18b-a, and 18 c-a define the line portion 12 a. The connection portions 18a-b, 18 b-b, and 18 c-b define the connection portion 12 b. Theconnection portions 18 a-c, 18 b-c, and 18 c-c define the connectionportion 12 c.

As illustrated in FIGS. 21 and 22, the external terminal 16 a preferablyis a rectangular or substantially rectangular conductor disposed nearthe center of the surface of the connection portion 18 a-b. Asillustrated in FIGS. 21 and 22, the external terminal 16 b preferably isa rectangular or substantially rectangular conductor disposed near thecenter of the surface of the connection portion 18 a-c. The externalterminals 16 a and 16 b are preferably made of a metal material such assilver or copper having low resistivity, for example. The surfaces ofthe external terminals 16 a and 16 b preferably are gold-plated.

As illustrated in FIG. 22, the signal line 20 is a linear conductordisposed in the dielectric body 12, and extends in the x-axis directionon the surface of the dielectric sheet 18 b. Both ends of the signalline 20 individually overlap the external terminals 16 a and 16 b inplan view from the z-axis direction. For example, the line width of thesignal line 20 preferably is in the range of about 100 μm to about 500μm, for example. In the present preferred embodiment, the line width ofthe signal line 20 preferably is about 240 μm, for example. The signalline 20 is made of a metal material such as silver or copper having lowresistivity.

As illustrated in FIG. 22, in the dielectric body 12, the groundconductor 22 (first ground conductor) is disposed between the signalline 20 and the first main surface (that is, in the positive z-axisdirection with respect to the signal line 20), and, more specifically,is disposed on the surface of the dielectric sheet 18 a nearest to thesurface of the dielectric body 12. The ground conductor 22 extends inthe x-axis direction on the surface of the dielectric sheet 18 a, andfaces the signal line 20 via the dielectric sheet 18 a. No opening isdisposed at a portion of the ground conductor 22 facing the signal line20. That is, the ground conductor 22 is a solid electrode thatcontinuously extends in the x-axis direction along the signal line 20 inthe line portion 12 a. The ground conductor 22 does not necessarily haveto completely cover the line portion 12 a. For example, in order to letgas caused by heat bonding of the dielectric sheet 18 made of athermoplastic resin escape, a small hole may be provided at apredetermined position on the ground conductor 22. The ground conductor22 is preferably made of a metal material such as silver or copperhaving low resistivity.

The ground conductor 22 includes the line portion 22 a and the terminalportions 22 b and 22 c. The line portion 22 a is disposed on the surfaceof the line portion 18 a-a, and extends in the x-axis direction. Theterminal portion 22 b is disposed on the surface of the line portion 18a-b, and preferably is a rectangular or substantially rectangular ringsurrounding the external terminal 16 a. The terminal portion 22 b isconnected to the end of the line portion 22 a in the negative x-axisdirection. The terminal portion 22 c is disposed on the surface of theline portion 18 a-c, and preferably is a rectangular or substantiallyrectangular ring surrounding the external terminal 16 b. The terminalportion 22 c is connected to the end of the line portion 22 a in thepositive x-axis direction.

As illustrated in FIG. 22, in the dielectric body 12, the groundconductor 24 (second ground conductor) is disposed between the signalline 20 and the second main surface (that is, in the negative z-axisdirection with respect to the signal line 20), and, more specifically,is disposed on the surface of the dielectric sheet 18 c. The groundconductor 24 is therefore disposed between the dielectric sheets 18 band 18 c. The ground conductor 24 extends in the x-axis direction on thesurface of the dielectric sheet 18 c, and faces the signal line 20 viathe dielectric sheet 18 b. That is, the ground conductor 24 faces theground conductor 22 via the signal line 20 sandwiched therebetween. Theground conductor 24 preferably is made of a metal material such assilver or copper having low resistivity, for example.

The ground conductor 24 includes the line portion 24 a and the terminalportions 24 b and 24 c. The line portion 24 a is disposed on the surfaceof the line portion 18 c-a, and extends in the x-axis direction. Theline portion 24 a has a ladder shape obtained by alternately disposing aplurality of openings 30 at which no conductive layer is provided and aplurality of bridge portions 60 at which a conductive layer is arrangedalong the signal line 20. As illustrated in FIGS. 22 and 24, theopenings are preferably rectangular or substantially rectangular inshape and overlap the signal line 20 in plan view from the z-axisdirection. Accordingly, the signal line 20 alternately overlaps theopenings 30 and the bridge portions 60 in plan view from the z-axisdirection. The openings 30 are arranged at regular intervals.

The terminal portion 24 b is disposed on the surface of the line portion18 c-b, and preferably is a rectangular or substantially rectangularring. The terminal portion 24 b is connected to the end of the lineportion 24 a in the negative x-axis direction. The terminal portion 24 cis disposed on the surface of the line portion 18 c-c, and preferably isa rectangular or substantially rectangular ring. The terminal portion 24c is connected to the end of the line portion 24 a in the positivex-axis direction.

As described previously, the signal line 20 is sandwiched between theground conductors 22 and 24 via the dielectric layers 18 a and 18 b.That is, the signal line 20 and the ground conductors 22 and 24 define atriplate strip line structure. As illustrated in FIG. 24, the distancebetween the signal line 20 and the ground conductor 22 is substantiallyequal to the thickness T1 of the dielectric sheet 18 a, and, forexample, preferably is in the range of about 50 μm to about 300 μm. Inthe present preferred embodiment, the distance between the signal line20 and the ground conductor 22 preferably is about 150 μm. On the otherhand, as illustrated in FIG. 24, the distance between the signal line 20and the ground conductor 24 is substantially equal to the thickness T2of the dielectric sheet 18 b, and, for example, preferably is in therange of about 10 μm to about 100 μm. In the present preferredembodiment, the distance between the signal line 20 and the groundconductor 24 preferably is about 50 μm, for example. That is, design isperformed so that the thickness T1 is larger than the thickness T2.

The via-hole conductor b1 passes through the connection portion 18 a-bof the dielectric sheet 18 a in the z-axis direction, and connects theexternal terminal 16 a and the end of the signal line 20 in the negativex-axis direction. The via-hole conductor b2 passes through theconnection portion 18 a-c of the dielectric sheet 18 a in the z-axisdirection, and connects the external terminal 16 b and the end of thesignal line 20 in the positive x-axis direction. As a result, the signalline 20 is connected between the external terminals 16 a and 16 b. Thevia-hole conductors b1 and b2 are preferably made of a metal materialsuch as silver or copper having low resistivity, for example.

The via-hole conductors B1 pass through the line portion 18 a-a of thedielectric sheet 18 a in the z-axis direction, and are disposed at theline portion 18 a-a. The via-hole conductors B2 pass through the lineportion 18 b-a of the dielectric sheet 18 b in the z-axis direction, andare disposed at the line portion 18 b-a. The via-hole conductor B1 andthe via-hole conductor B2 are connected to each other, so that a singlevia-hole conductor is provided and connects the ground conductors 22 and24. The via-hole conductors B1 and B2 are preferably made of a metalmaterial such as silver or copper having low resistivity.

The protection layer 14 covers the substantially entire surface of thedielectric sheet 18 a. As a result, the protection layer 14 covers theground conductor 22. The protection layer 14 preferably is made of aflexible resin such as a resist material, for example.

As illustrated in FIG. 22, the protection layer 14 includes the lineportion 14 a and the connection portions 14 b and 14 c. The line portion14 a covers the entire surface of the line portion 18 a-a, therebycovering the line portion 22 a.

The connection portion 14 b is connected to the end of the line portion14 a in the negative x-axis direction, and covers the surface of theconnection portion 18 a-b. At the connection portion 14 b, the openingsHa to Hd are provided. The opening Ha preferably is a rectangular orsubstantially rectangular opening located at the center of theconnection portion 14 b. The external terminal 16 a is exposed to theoutside via the opening Ha. The opening Hb preferably is a rectangularor substantially rectangular opening arranged in the positive y-axisdirection with respect to the opening Ha. The opening Hc preferably is arectangular or substantially rectangular opening arranged in thenegative x-axis direction with respect to the opening Ha. The opening Hdpreferably is a rectangular or substantially rectangular openingarranged in the negative y-axis direction with respect to the openingHa. The terminal portion 22 b is exposed to the outside via the openingsHb to Hd so as to define and function as an external terminal.

The connection portion 14 c is connected to the end of the line portion14 a in the positive x-axis direction, and covers the surface of theconnection portion 18 a-c. At the connection portion 14 c, the openingsHe to Hh are provided. The opening He preferably is a rectangular orsubstantially rectangular opening located at the center of theconnection portion 14 c. The external terminal 16 b is exposed to theoutside via the opening He. The opening Hf preferably is a rectangularor substantially rectangular opening arranged in the positive y-axisdirection with respect to the opening He. The opening Hg preferably is arectangular or substantially rectangular opening arranged in thepositive x-axis direction with respect to the opening He. The opening Hhpreferably is a rectangular or substantially rectangular openingarranged in the negative y-axis direction with respect to the openingHe. The terminal portion 22 c is exposed to the outside via the openingsHf to Hh so as to define and function as an external terminal.

The adhesive layer 70 preferably is made of an insulating adhesive, andis located on the first main surface of the dielectric body 12. Morespecifically, the adhesive layer 70 is arranged so that it extends inthe x-axis direction on the line portion 14 a of the protection layer 14in the dielectric body 12. The cover sheet 72 preferably is a flexiblesheet that is releasably attached to the adhesive layer 70. For example,the adhesive layer 70 and the cover sheet 72 define an adhesive tapewith a cover sheet thereon.

The connectors 100 a and 100 b are disposed on the surfaces of theconnection portions 12 b and 12 c, respectively. The descriptions of thestructures of the connectors 100 a and 100 b have been provided above,and will be therefore omitted.

The high-frequency signal transmission line 10 g is preferably used asdescribed below with reference to FIGS. 5A, 5B, 6A, 6B, and 25. FIG. 25is a cross-sectional view of the electronic apparatus 200.

The electronic apparatus 200 preferably includes the high-frequencysignal transmission line 10 g, the circuit boards 202 a and 202 b, thereceptacles 204 a and 204 b, the battery pack (article) 206, and thecasing 210.

At the circuit board 202 a, for example, a transmission circuit or areceiving circuit including an antenna is disposed.

At the circuit board 202 b, for example, a feeding circuit is disposed.The battery pack 206 is, for example, a lithium-ion secondary battery,and the surface of the battery pack 206 is covered with an insulator.The circuit board 202 a, the battery pack 206, and the circuit board 202b are arranged in this order from the negative x-axis direction to thepositive x-axis direction.

The receptacles 204 a and 204 b are disposed on the main surfaces of thecircuit boards 202 a and 202 b in the negative z-axis direction,respectively. The connectors 100 a and 100 b are connected to thereceptacles 204 a and 204 b, respectively. As a result, a high-frequencysignal having the frequency of, for example, 2 GHz transmitted betweenthe circuit boards 202 a and 202 b is applied to the center conductors108 of the connectors 100 a and 100 b via the receptacles 204 a and 204b. The external conductors 110 of the connectors 100 a and 100 b areheld at the ground potential via the circuit boards 202 a and 202 b andthe receptacles 204 a and 204 b, respectively. As a result, thehigh-frequency signal transmission line 10 g electrically and physicallyconnects the circuit boards 202 a and 202 b.

As illustrated in FIG. 25, the high-frequency signal transmission line10 g is fixed to the battery pack 206 via the adhesive layer 70 fromwhich the cover sheet 72 has been detached. The surface of thedielectric body 12 is a main surface located on the side of the groundconductor 22 with respect to the signal line 20. Accordingly, betweenthe signal line 20 and the battery pack 206, there is the groundconductor 22 that is a solid conductor (that continuously extends in thex-axis direction).

The high-frequency signal transmission line 10 g preferably is bonded tothe battery pack 206, but may be bonded to a printed circuit board orthe casing of an electronic apparatus. The surface of the battery pack206 preferably is covered with an insulator, but may be covered with aconductor such as metal.

An exemplary method of bonding the high-frequency signal transmissionline 10 g to the battery pack 206 will be described below with referenceto the accompanying drawings. FIG. 26 is a cross-sectional view of thehigh-frequency signal transmission line 10 g and the battery pack 206 towhich the high-frequency signal transmission line 10 g is bonded.

First, as illustrated in FIG. 21, the cover sheet 72 is partly detachedfrom the adhesive layer 70. The exposed portion of the adhesive layer 70is bonded to the battery pack 206.

Subsequently, as illustrated in FIG. 26, the adhesive layer 70 is bondedto the battery pack 206 while detaching the cover sheet 72 from theadhesive layer 70. Thus, the high-frequency signal transmission line 10g is bonded to the battery pack 206 using a procedure similar to aprocedure for the placement of a sticky label. Referring to FIG. 26, thestructures of the ground conductors 22 and 24 and the signal line 20 arepartly illustrated.

The high-frequency signal transmission line 10 g having theabove-described structure can be fixed to an article in a narrow space.More specifically, components such as a fixing bracket and a screw forfixing the high-frequency signal transmission line 10 g to an articlebecomes unnecessary. As a result, the high-frequency signal transmissionline 10 g can be fixed to an article in a narrow space in an electronicapparatus. Furthermore, since a screw for fixing the high-frequencysignal transmission line 10 g to an article is not used, no screw holeis formed at the battery pack 206.

As illustrated in FIG. 26, in the high-frequency signal transmissionline 10 g, the adhesive layer 70 is bonded to the battery pack 206 whiledetaching the cover sheet 72 from the adhesive layer 70. Thus, thehigh-frequency signal transmission line 10 g is bonded to the batterypack 206 using a procedure similar to a procedure for the placement of asticky label. Accordingly, in the high-frequency signal transmissionline 10 g, it is unnecessary to perform screwing with a fixed structurefor the coaxial cable disclosed in Japanese Unexamined PatentApplication Publication No. 2007-123740. The high-frequency signaltransmission line 10 g can be easily fixed to the battery pack 206.

Since the high-frequency signal transmission line 10 g does not needcomponents such as a fixing bracket and a screw, no stray capacitance isgenerated between the signal line 20 and each of the fixing bracket andthe screw. Accordingly, the deviation of the characteristic impedance ofthe high-frequency signal transmission line 10 g from a predeterminedcharacteristic impedance is significantly reduced and prevented.

The structure of a high-frequency signal transmission line according tothe first modification of the second preferred embodiment of the presentinvention will be described below with reference to the accompanyingdrawing. FIG. 27 is an exploded view of the laminate 12 in ahigh-frequency signal transmission line 10 h according to the firstmodification.

Like the high-frequency signal transmission line 10 h illustrated inFIG. 27, the high-frequency signal transmission line 10 a may includethe adhesive layer 70 and the cover sheet 72.

A high-frequency signal transmission line according to the secondmodification of the second preferred embodiment of the present inventionwill be described below with reference to the accompanying drawing. FIG.28 is an exploded view of the laminate 12 in a high-frequency signaltransmission line 10 i according to the second modification.

Like the high-frequency signal transmission line 10 i illustrated inFIG. 28, the high-frequency signal transmission line 10 b may includethe adhesive layer 70 and the cover sheet 72.

A high-frequency signal transmission line according to the thirdmodification of the second preferred embodiment of the present inventionwill be described below with reference to the accompanying drawing. FIG.29 is an exploded view of the laminate 12 in a high-frequency signaltransmission line 10 j according to the third modification.

Like the high-frequency signal transmission line 10 j illustrated inFIG. 29, the high-frequency signal transmission line 10 c may includethe adhesive layer 70 and the cover sheet 72.

A high-frequency signal transmission line according to the fourthmodification of the second preferred embodiment of the present inventionwill be described below with reference to the accompanying drawing. FIG.30 is an exploded view of the laminate 12 in a high-frequency signaltransmission line 10 k according to the fourth modification.

Like the high-frequency signal transmission line 10 k illustrated inFIG. 30, the high-frequency signal transmission line 10 d may includethe adhesive layer 70 and the cover sheet 72.

A high-frequency signal transmission line according to the fifthmodification of the second preferred embodiment of the present inventionwill be described below with reference to the accompanying drawing. FIG.31 is an exploded view of the laminate 12 in a high-frequency signaltransmission line 101 according to the fifth modification.

Like the high-frequency signal transmission line 101 illustrated in FIG.31, the high-frequency signal transmission line 10 e may include theadhesive layer 70 and the cover sheet 72.

A high-frequency signal transmission line according to the sixthmodification of the second preferred embodiment of the present inventionwill be described below with reference to the accompanying drawing. FIG.32 is an exploded view of the laminate 12 in a high-frequency signaltransmission line 10 m according to the sixth modification.

Like the high-frequency signal transmission line 10 m illustrated inFIG. 32, the high-frequency signal transmission line 10 f may includethe adhesive layer 70 and the cover sheet 72.

A high-frequency signal transmission line according to the seventhmodification of the second preferred embodiment of the present inventionwill be described below with reference to the accompanying drawings.FIG. 33 is an external perspective view of a high-frequency signaltransmission line 10 n according to the seventh modification. FIG. 34 isan exploded view of the dielectric body 12 in the high-frequency signaltransmission line 10 n illustrated in FIG. 33. FIG. 35 is across-sectional view of the high-frequency signal transmission line 10 nillustrated in FIG. 33.

The difference between the high-frequency signal transmission lines 10 nand 10 g is that the adhesive layer 70 is partly absent and a pad 74 isdisposed. More specifically, as illustrated in FIGS. 33 and 34, the lineportion 14 a of the protection layer 14 and the adhesive layer 70 arepartly absent. The pad 74 made of solder is preferably provided at aposition at which the line portion 14 a of the protection layer 14 andthe adhesive layer 70 are absent. The pad 74 is provided on the groundconductor 22, and is connected to the ground conductor 22.

As illustrated in FIG. 35, the high-frequency signal transmission line10 n having the above-described structure is fixed to the battery pack206 covered with a metal cover via the adhesive layer 70. At that time,the pad 74 is in contact with the metal cover of the battery pack 206.As a result, the ground conductor 22 is electrically connected to themetal cover of the battery pack 206 via the pad 74. Under the conditionthat the metal cover is held at a ground potential, the ground conductor22 is held at the ground potential not only via the connectors 100 a and100 b but also via the metal cover. That is, the potential of the groundconductor 22 is more stably brought close to the ground potential.

Instead of the metal cover of the battery pack 206, the pad 74 may be incontact with the metal casing of an electronic apparatus or the land ofa printed circuit board.

A high-frequency signal transmission line according to the eighthmodification of a preferred embodiment of the present invention will bedescribed below with reference to the accompanying drawings. FIG. 36 isan external perspective view of a high-frequency signal transmissionline 10 o according to the eighth modification. FIG. 37 is an explodedview of the dielectric body 12 in the high-frequency signal transmissionline 10 o illustrated in FIG. 36. FIG. 38 is a cross-sectional view ofthe high-frequency signal transmission line 10 o illustrated in FIG. 36.

The difference between the high-frequency signal transmission lines 10 oand 10 g is that the adhesive layer 70 is a conductive adhesive. Morespecifically, as illustrated in FIGS. 36 and 37, a part of the lineportion 14 a of the protection layer 14 is absent. The ground conductor22 is therefore disposed on the first main surface of the dielectricbody 12. At a position at which the line portion 14 a is absent, theadhesive layer 70 and the cover sheet 72 are provided. As a result, theadhesive layer 70 is provided on the ground conductor 22, and isconnected to the ground conductor 22.

As illustrated in FIG. 38, the high-frequency signal transmission line10 o having the above-described structure is fixed to the battery pack206 covered with a metal cover (conductive portion) via the adhesivelayer 70. At that time, the adhesive layer 70 is in contact with themetal cover of the battery pack 206. As a result, the ground conductor22 is electrically connected to the metal cover of the battery pack 206via the adhesive layer 70. Under the condition that the metal cover isheld at a ground potential, the ground conductor 22 is held at theground potential not only via the connectors 100 a and 100 b but alsovia the metal cover. That is, the potential of the ground conductor 22is more stably brought close to the ground potential.

A high-frequency signal transmission line according to the ninthmodification of a preferred embodiment of the present invention will bedescribed below with reference to the accompanying drawings. FIG. 39 isan external perspective view of a high-frequency signal transmissionline 10 p according to the ninth modification. FIG. 40 is an explodedview of the dielectric body 12 in the high-frequency signal transmissionline 10 p illustrated in FIG. 39. FIG. 41 is a cross-sectional view ofthe high-frequency signal transmission line 10 p illustrated in FIG. 39.

As illustrated in FIGS. 39 and 40, the difference between thehigh-frequency signal transmission lines 10 p and 10 o is that each ofthe adhesive layer 70 and the cover sheet 72 is divided into twoportions.

As illustrated in FIG. 41, the high-frequency signal transmission line10 p having the above-described structure is fixed to a printed circuitboard 306 with a land (conductive portion) 307 thereon via the adhesivelayer 70. The land 307 is obtained preferably by applying a coating 309to a base electrode 308 made of, for example, Cu. The adhesive layer 70is in contact with the land 307. As a result, the ground conductor 22 iselectrically connected to the land 307 via the adhesive layer 70. Underthe condition that land 307 is held at a ground potential, the groundconductor 22 is held at the ground potential not only via the connectors100 a and 100 b but also via the land 307. That is, the potential of theground conductor 22 is more stably brought close to the groundpotential.

Since the adhesive layer 70 is divided into a plurality of portions, theoccurrence of wrinkles and sagging at the high-frequency signaltransmission line 10 p is significantly reduced and prevented at thetime of placement of the high-frequency signal transmission line 10 p.The two adhesive layers are preferably in contact with an article suchas a land so that they are held at a ground potential. Only one of thetwo adhesive layers may be held at the ground potential, or none of themmay be connected to the ground.

A high-frequency signal transmission line according to the tenthmodification of a preferred embodiment of the present invention will bedescribed below with reference to the accompanying drawing. FIG. 42 isan exploded view of the dielectric body 12 in a high-frequency signaltransmission line 10 q according to the tenth modification.

The difference between the high-frequency signal transmission lines 10 qand 10 o is that the ground conductor 24 is disposed on the undersurfaceof the dielectric sheet 18 b. More specifically, the signal line 20 isdisposed on the surface of the dielectric sheet 18 b, and the groundconductor 24 is disposed on the undersurface of the dielectric sheet 18b. In the high-frequency signal transmission line 10 q, the dielectricsheet 18 c is not provided and a protection layer 15 is provided.

Since the high-frequency signal transmission line 10 q having theabove-described structure preferably includes only two dielectric sheets18, the high-frequency signal transmission line 10 q can be easilycreated.

Other Preferred Embodiments

A high-frequency signal transmission line according to the presentinvention is not limited to the high-frequency signal transmission lines10 and 10 a to 10 q according to the above-described preferredembodiments of the present invention and modifications thereof, andvarious changes can be made to these high-frequency signal transmissionlines without departing from the scope of the present invention.

In the high-frequency signal transmission lines 10 and 10 a to 10 q, aplurality of openings 30 preferably have the same shape, but may havedifferent shapes. For example, the length of a predetermined one of theopenings 30 in the x-axis direction may be longer than that of the otherones of the openings 30 in the x-axis direction. As a result, in aregion where the predetermined one of the openings 30 is formed, thehigh-frequency signal transmission lines 10 and 10 a to 10 q can beeasily bent.

The structures of the high-frequency signal transmission lines 10 and 10a to 10 q may be combined.

In the high-frequency signal transmission lines 10 a to 10 q, thecharacteristic impedance of the signal line 20 preferably changes suchthat, with increasing proximity to the other one of two adjacent bridgeportions 60 from one of them, the characteristic impedance increases inthe order of the minimum value Z2, the intermediate value Z3, and themaximum value Z1 and then decreases in the order of the maximum valueZ1, the intermediate value Z3, and the minimum value Z2. However, thecharacteristic impedance of the signal line 20 may change such that,with increasing proximity to the other one of two adjacent bridgeportions 60 from one of them, the characteristic impedance increases inthe order of the minimum value Z2, the intermediate value Z3, and themaximum value Z1 and then decreases in the order of the maximum valueZ1, an intermediate value Z4, and the minimum value Z2. That is, thedifferent intermediate values Z3 and Z4 may be used. For example, eachof the openings 30, 31, 44 a, and 44 may not be symmetric with respectto the line A. The intermediate value Z4 needs to be larger than theminimum value Z2 and smaller than the maximum value Z1.

Between two adjacent bridge portions 60, different minimum values Z2 maybe obtained. That is, on the condition that the high-frequency signaltransmission lines 10 a to 10 q have the predetermined characteristicimpedance, the minimum values Z2 do not necessarily have to be the same.However, the minimum value Z2 obtained in one of the bridge portions 60is preferably smaller than the intermediate value Z3, and the minimumvalue Z2 obtained in the other one of the bridge portions 60 ispreferably smaller than the intermediate value Z4.

The adhesive layer 70 and the cover sheet 72 may further be provided onthe second main surface of the dielectric body 12.

As described previously, preferred embodiments of the present inventionare useful for a high-frequency signal transmission line and anelectronic apparatus, and, in particular, provide an advantage in termsof suitability to fix a high-frequency signal transmission line to anarticle in a narrow space.

While preferred embodiments of the present invention have been describedabove, it is to be understood that variations and modifications will beapparent to those skilled in the art without departing from the scopeand spirit of the present invention. The scope of the present invention,therefore, is to be determined solely by the following claims.

What is claimed is:
 1. An electronic apparatus comprising ahigh-frequency signal transmission line and a metal article that aredisposed in a casing, the high-frequency signal transmission linecomprising: a laminate that is obtained by laminating insulating layersand has a first main surface and a second main surface; a linear signalline disposed in the laminate; a first ground conductor that is disposedin the laminate, faces the signal line via one of the insulating layers,and continuously extends along the signal line, wherein in a portion ofthe first ground conductor facing the signal line substantially, noopening is disposed and wherein the first ground conductor is locatednear the first main surface with respect to the signal line; and asecond ground conductor that is disposed in the laminate, faces thefirst ground conductor via the signal line sandwiched therebetween, andhas a plurality of openings arranged along the signal line, wherein thesecond ground conductor is located near the second main surface withrespect to the signal line; wherein the linear signal line, the firstground conductor and the second ground conductor define a striplinehaving a triplate structure; wherein a main surface of thehigh-frequency signal transmission line near the first ground conductorwith respect to the signal line is in contact with the metal article;and wherein a main surface of the high-frequency signal transmissionline near the second ground conductor with respect to the signal line isopposed to the casing at a specified distance.
 2. The electronicapparatus according to claim 1, wherein the first main surface is fixedto the article.
 3. The electronic apparatus according to claim 1,wherein the first ground conductor is electrically connected to themetal article.
 4. The electronic apparatus according to claim 1, whereinthe first ground conductor is disposed on one of the insulating layersnearest to the first main surface; and wherein the second groundconductor is disposed between ones of the insulating layers.
 5. Theelectronic apparatus according to claim 1, wherein the laminate furtherincludes a protection layer covering the first ground conductor.
 6. Theelectronic apparatus according to claim 1, further comprising aconnector that is attached to the laminate and includes a signalterminal electrically connected to the signal line and a ground terminalelectrically connected to the first ground conductor and the secondground conductor.
 7. The electronic apparatus according to claim 1,wherein the plurality of openings are arranged at regular intervals. 8.The electronic apparatus according to claim 1, wherein the second groundconductor has a ladder shape obtained by alternately forming theplurality of openings and bridge portions along the signal line; andwherein a characteristic impedance of the signal line changes betweentwo adjacent ones of the bridges in such a manner that, with increasingdistance from one of the two adjacent bridge portions and withdecreasing distance to the other bridge portion, the characteristicimpedance increases in an order of a minimum value, a first intermediatevalue, and a maximum value and then decreases in an order of the maximumvalue, a second intermediate value, and the minimum value.
 9. Theelectronic apparatus according to claim 1, wherein the laminate hasflexibility.
 10. The electronic apparatus according to claim 1, furthercomprising: an adhesive layer formed on the first main surface; and acover layer releasably attached to the adhesive layer; wherein thehigh-frequency signal transmission line is fixed to the article via theadhesive layer from which the cover layer has been detached.
 11. Theelectronic apparatus according to claim 10, wherein the first groundconductor is disposed on the first main surface; and wherein theadhesive layer is made of a conductive adhesive, and is formed on thefirst ground conductor.
 12. The electronic apparatus according to claim11, wherein the article has a conductive portion; and wherein the firstground conductor is electrically connected to the conductive portion ofthe article via the adhesive layer.
 13. The electronic apparatusaccording to claim 11, wherein the metal article is maintained at aground potential.
 14. An electronic apparatus comprising ahigh-frequency signal transmission line and a metal article that aredisposed in a casing, the high-frequency signal transmission linecomprising: an element assembly having a first main surface and a secondmain surface; a linear signal line disposed in the element assembly; alinear signal line disposed in the element assembly; a first groundconductor that is disposed on a side of the first main surface withrespect to the signal line in the element assembly and faces the signalline, wherein in a portion of the first ground conductor facing thesignal line, substantially no opening is disposed; and a second groundconductor that faces the first ground conductor via the signal linesandwiched therebetween in the element assembly, and has an openingarranged along the signal line, wherein the second ground conductor islocated near the second main surface with respect to the signal line;and an adhesive layer formed on the first main surface; wherein thelinear signal line, the first ground conductor and the second groundconductor define a stripline having a triplate structure; wherein thehigh-frequency signal transmission line is fixed to the article via theadhesive layer; and wherein a main surface of the high-frequency signaltransmission line near the second ground conductor with respect to thesignal line is opposed to the casing at a specified distance.